The legend of vampires has existed, in one form or another, as long as there have been legends. From China to Ireland- in nearly every region of the world- there is some version of the vampire legend. There are those who believe that Biblical references to 'screech owl' are actually comments about vampirism, since the word in Latin, strix, also means 'vampire'. The myths existed in ancient Babylon, and references have been found in ancient Assyrian and Chaldean tablets. Which, in a way, is disturbing. It makes absolutely no sense that similar ancient legends should exist in such diverse lands, unless there is some truth to those legends, some inspiration for them. Food for thought, at least.
Perhaps more so than any other supernatural legend, vampires owe much of their popularity, and certainly their endurance, to literature and the media. Though a number of writers had taken a crack at the vampire story before him, Bram Stoker certainly wrote the definitive vampire story in 1987 -Dracula. For many decades thereafter, Stoker's work set the 'rules' in place for vampire tales. Though the myriad legends around the world each had their own wildly variant concepts about how vampires were created, what their weaknesses were etc, there were now hard and fast rules.
Vampires could not be seen in mirrors. They cast no shadows. They could not cross running water, and direct sunlight could destroy them. They commanded the low creatures, bats and rats and wolves, and they could transform themselves into these creatures. They slept in beds of their native earth. They had a powerful hypnotic gaze and could transform another person into a vampire by draining the blood from a living human, who would then, after death, rise from the grave. They feared the crucifix and garlic, and holy water could burn them. A stake through the heart and decapitation were the appropriate combination to kill a vampire once and for all.
Despite film and television creators and writers having worked their own twists on this basic formula for decades, the average consumer of Western pop culture still likely accepts Stoker’s as an unassailable truth. Novelists such as Kim Newman, Dan Simmons and particularly Anne Rice (Interview with a Vampire etc) have radically altered those rules in creating their own vampire mythologies.
"To make you a vampire, they have to suck your blood and then you have to suck their blood; its like a whole big sucking thing. Mostly their just gonna kill you, just take all your blood."
Buffy in 'Welcome to the Hellmouth.'
When the time came for Joss Whedon to invent the mythology for BtVS, he chose what suited him. The greatest diversion from stoker's formula is that Whedon went back to an interpretation of ancient vampire mythology that few but scholars remember: some legends say that vampires are not humans at all, but demons who have taken up residence inside human corpses. From there, Whedon has built his own monsters. Built a better vampire, some might say, particularly since these vampires are not quite as all-powerful as their legendary and fictional forefathers.
Buffy, to Ford, in 'Lie to Me'.
Vampires, in the world of Buffy, cannot fly. They cannot turn into mist. They cannot shape-shift at all. Though they cast no reflection in mirrors, they do cast shadows. In addition, they can be videotaped. While they do not actually need to breath- at least not in the sense that humans do, with and intake of oxygen, their lungs do perform a function that stimulates breathing. One possibility is that this procedure fouls whatever oxygen they do thake in. It seems likely that the false act of 'breathing' is somehow a comfort to them- and perhaps makes them feel less like the living dead.
Whedon's vampires have a capacity for hypnosis, but some are much more skilled in its uses than others. Drusilla, for one, uses her hypnosis in Becoming, Parts 1 and 2 to great effect, mesmerising Giles into giving up valuable information and distracting Kendra long enough to cut her throat.
"Xander, listen to me. Jesse is dead. You have to remember that your not looking at your friend, your looking at the thing that killed him."
Giles, in 'The Harvest.'"A vampire isn't a person at all. It may have the movements, the memories, even the personality of the person it takes over, but it is a demon at the core, there's no halfway."
Giles in 'Angel'.
Like Stoker's vampires, Whedon's cannot enter a private home without an invitation, but once they have been invited, in they can return at any time. The traditional vampire cannot enter houses of worship and they fear religious symbols, particularly the Christian cross.
The Master, about the crucifix, in 'Nightmares'.
Whedon's creations have no problem entering a church (see 'Superstar', Season 4) but touching consecrated earth gives them great suffering, and they do fear the cross. One thing Whedon' vampires share with Stokers that many other creative imaginations have ignored over the years is the exposure to sunlight. In most recently created vampire mythologies, the sunlight will actually destroy a vampire. But for both Whedon and Stoker, in order for the sun to kill a vampire, it must be direct light. A heavily overcast day (see 'Amends'; the snow saves Angel from the sunrise) or some other kind of covering (see 'Becoming') is sufficient to keep the creature alive for a period of time.
In addition, vampires have frequently been portrayed as having almost instant healing abilities, save for the stake through the heart. Whedon's vampires ca recover from just about anything, but it takes a lot longer to get there. Hence Spike in a wheelchair for a lot of Season Two, and Darla's comment in 'Angel' that "Bullets can't kill vampires, but that can hurt them like hell..."
As to the origins of the vampires themselves, Whedon, through the character of the Watcher, Rupert Giles, has a very specific idea of their origins:
"This world is older than any of you know, and contrary to popular mythology, it did not begin in paradise. For untold eons, demons walked the earth, made it their home, their Hell. In time, they lost their touch with reality, and the way was made for mortal animals. For Man. What remains of the Old Ones are vestiges: certain magiks, certain creatures..."
"The books tell that the last demon to leave this reality fed off a human, and mixed their blood. He was a human possessed- infected- by the demon's soul. He bit another and another...and so they walk the earth, feeding. Killing some, mixing their blood with others to make more of their kind. Waiting for the animals to die out and the old ones to return."
Towards the goal of returning their ancient ancestors to the Earth, the demons who reside within the vampires have created their own 'families' and societies, tribes or clans of vampires who work and live together to further their chaotic impulses. As Buffy points out in 'Lie to Me' however, 'vampires are kind of picky about who they change.' Frequently, a clan will include a group of vampires and their 'sire', the vampire who turned them into vampires in the first place. The best known vampire clan in the Buffy mythology is the Order of Aurelius, which was lead by the master for centuries and whose Brethren, or adherents, have included Angel and Darla, and by implication, very likely Spike and Drusilla as well.
Indeed, Joss Whedon seems to have purposefully moved away from the vampire fictions of recent years, finding a middle ground between the ancient legends, Bram Stoker's 'rules', and his own unique twist on the subject. Witness, for example, the following exchange from 'School Hard':
Angel: "I taught you to always guard your perimeter. You should have someone out there."
Spike: "I did, I’m surrounded by idiots. What's new with you?"
Angel: "Everything."
Spike: "Come up against the Slayer yet?"
Angel: "She's cute. Not too bright, though. Gave her the puppy-dog, I', all tortured act. Keeps her off my back while I feed."
Spike: "People still fall for that Anne Rice routine? What is the world coming to?"
Joss, we wait in suspense for anything else you wish to throw at us.